MDS Business Rule that changes Domanin-Based attribute does not work. BUG ?

Edit: Another way to ask this: how do I create a Business Rule to Clear a Domain-Based Entity that is pointing to same Entity (table).

Or I could take pointing to itself.   I've tried setting it blank, to Code from Entity and both give error.  I disabled all other rules, so this is the only 1 I am testing, and I do publish it after creation...  I could maybe create a workflow for this, but that does not sound reasonable.

NEED HELP !  

In General I've tried many variations and none worked.

My Code is a string not an int. 

So say I have

Code Name Something dPointer

1A      Name1     s          ___

1B      Name2      de       1C

1C      Name2     ss         ___

So I am tying to make a rule, when Something changes dPointer is cleared. ( in example above if I set line 2s Something value to dx 1C should go ___  ie blank.)

IF
    Something has changed in group 1
THEN
    dPointer equals Blank

I get an error when running that ~NULL~ can't be set to int. ie the Blank its trying to insert is for nvchar ...

Also trying to set dPointer to a dummy record that holds a blank also does not work as then the erro is something like cant set int to nvchar (as my Code is a string)...